Acid sensing ion channels (ASICs) are proton-gated cationic channels expressed in the central and peripheral nervous systems. The ASIC family in humans includes ASIC1, ASIC2, ASIC3 and ASIC4 subunits which arrange into homo- or heteromultimeric ion channels in neuronal membranes. ASIC1, ASIC2 and ASIC3 are significantly expressed in the small and medium nociceptive sensory neurons that are able to detect noxious chemical, thermal, and high threshold mechanical stimuli. ASIC2 and ASIC3 are also expressed in large neurons that mostly correspond to low threshold mechanoreceptors.
ASICs are permeable to Na+ and Ca2+ ions and are activated by external pH variations ranging from pH 6.8 to 4.0. ASICs are believed to play an important role in sensing local acidosis. Local tissue acidosis is a hallmark of pain and inflammation, and inflamed tissues frequently exhibit low pH (as low as ˜4.7). Blockage of ASICs has been proposed as a method for treating a variety of disorders and conditions. Blockage of ASIC1 in particular has been proposed as a means for treating conditions such as pain, neurodegenerative diseases, and psychiatric diseases.
Pharmacologic inhibitors of ASIC1 include the tarantula peptide Psalmotoxin-1 (PcTx1) which specifically inhibits ASIC1 homomers, and the small molecule, non-selective ASIC inhibitors amiloride and A-317567. The 40 amino acid peptide toxin APETx2, isolated from sea anemone, has been shown to inhibit ASIC3 homomers as well as ASIC3/1 and ASIC3/2 heteromers.
Currently, there are no known antibodies that specifically block ASICs. Thus, there is a need in the art for novel ASIC inhibitors, such as anti-ASIC1 antibodies, that can be used to treat diseases and conditions mediated by ASIC signaling.